Prior proportional variable force solenoids typically require very close tolerances and precise adjustment of the air gap between the armature and a pole piece in order to attempt to achieve proportional control characteristics.
Other such solenoids involve the use of a trunk pole piece in order that the magnetic field operating on the armature is a function solely of flux density rather than a combination of magnetic circuit permeance and flux density. The trunk pole piece is adjustable in order to change the core gap to achieve proportional control. In addition to the additional bulk, complexity and cost of employing a pole piece, such prior art devices are expensive to manufacture and require close manufacturing tolerances.
It is an object of the invention to eliminate the need to maintain the close manufacturing tolerances associated with the air gap in a solenoid while also eliminating the need for an adjustable air gap.
Another object of this invention is to significantly reduce the cost of manufacture of a proportional variable force solenoid operated valve while maintaining substantially linear proportional control.
It is a further object of this invention to simplify the design and assembly of such solenoid control valves.
It is also an object of this invention to improve the reliability of such solenoid operated valves.
It is yet a further object of this invention to reduce the size of a proportional variable force solenoid operated valve.